Forget about wishing for the sun. It won't return to most beach areas until Friday, says the National Weather Service. The marine layer is thick and is expected to extend 10 miles inland by Thursday morning. Temperatures could be upwards of 10 degrees below normal.

"We've had an unusual number of troughs of low pressure moving through in July," says Ivory Small, chief science officer at the weather service in Rancho Bernardo.

There have been clear skies at Lindbergh Field only four days this month, half the average for July. And Lindbergh is running 4.3 temperatures below normal for July.

The coastal regional also is being affected by a strong 'inversion layer.' The term refers to a temperature inversion. The temperature increases the higher you go in the atmosphere, up to a point. And the inversion can greatly affect our weather. Today, the temperature above 2,100 foot level was in the low-to-mid 70s at 9 a.m. The temperature was in the 60s, near the surface, at the coast. The warmer air aloft results in less atmospheric mixing, which allows the marine layer to stay in place longer.

Local knowledge: For newcomers to places like San Diego's Bankers Hill, the sound of jets landing at Lindbergh Field might sound amplified tonight because some of the noise is trapped by the low coastal clouds.

Fast facts: San Diego's Lindbergh Field has recorded clear skies on only four of the first 20 days this month. During an average July, the figure would be about twice as high.

Cautionary note: Strong rip currents are expected Wednesday, especially in north county, where waves could rise to 9 feet from Oceanside to Carlsbad. The surf will be in the 3 foot range in south county, but will hit at an angle that'll also cause rips.